It is known (see U.S. Pat. Nos. 4,263,260 and 4,339,413 and patents in the corresponding class of the Manual of Patent Examining Classification) to provide catalytic reactors, especially for exothermic reactions, but also for endothermic reactions, in which the catalyst bed is formed by particles, granules or shaped bodies of a catalyst material and this bed is penetrated in whole or in part by tubes, e.g. for heating or cooling the bed and/or for feeding reactants to the bed or removing reaction products therefrom.
Such tube-bundle reactors may make use of rectilinear tubes or tubes defining helical or spiral patterns and forming a tube bundle in the interstices of which the catalyst bed can be provided.
Typical of the exothermic and endothermic catalytic reactions, which can be carried out in such reactors, is methanol synthesis, methanization and ammonia synthesis.
In general, the catalytic reaction occurs on the surface of the subdivided catalyst material with the excess heat thereby generated being conducted away by a cooling fluid circulated through the tubes or with heat required to trigger the reaction or to maintain it being delivered by a heating fluid circulated through these tubes.
The tubes thus serve to abstract excess heat or to supply heat necessary for the desired reaction so that by-product formation and side reactions are suppressed.
At the upper end lower ends of the reactor, the tubes of the tube bundle generally terminate at so-called tube sheets or in other manifold structures which allow the cooling or heating fluid to be distributed to the tubes at an inlet side of the tube bundle and depleted fluid to be collected at an outlet side of this tube bundle.
The tube sheet, at least at the bottom of the reactor, generally forms a support for the catalyst bed.
Reactors of this type have been found to be highly efficient and indeed are widely used. From time to time, however, the operation of such reactors must be interrupted, e.g. to replace a catalyst whose activity has deteriorated beyond an economical degree. In this case, the depleted catalyst must be discharged from the housing and replaced by fresh catalyst.
This discharge of the depleted catalyst poses problems. Although the interstices and openings provided for the discharge of the catalyst and the movement of the particles between the tubes of the tube bundle generally are sufficiently large to enable the particles to pass through a more or less friction less flow, in practice the tubes, especially in the region of the discharge opening, tend to obstruct such movement.
For effective operation of the catalytic reactor and for various structural reasons, it is imperative that the turns of the tube bundle or the layers of the tube bundle be as close together as possible and ultimately of the same order of magnitude as the diameter of the particles of the catalyst bed which are distributed in the interstices between the tubes.
When the discharge opening in the housing is unblocked to discharge the catalyst bed, the initial flow of the catalyst particles is relatively free of pressure drops from the catalyst above, which is no longer supported by the catalyst particles below. The particles ten to bridge across the tubes and these bridges obstruct the further flow of the catalyst particles.
The discharge of catalysts from such a reactor must be continuously assisted by mechanical or manual means, thereby making the discharge process labor intensive and time-consuming. This of course means that operation of the catalytic reactor is unduly complicated and expensive.